Abstract

The initial host response in a primary chlamydial infection is the onset of acute inflammation. However, we still know very little about the early temporal events in the induction of the acute inflammatory response and how these events relate to the initial chlamydial developmental cycle in an actual genital infection. Because it was critical to initiate a synchronous infection in the endocervix in the first 24 h to evaluate the sequential expression of the host response, we developed the surgical methodology of depositing Chlamydia muridarum directly on the endocervix. Cervical tissue was collected at 3, 12, and 24 h after inoculation and the expression array of chemokines, cytokines, and receptors was assessed to characterize the response during the initial developmental cycle. Polymorphonuclear leukocyte (PMN) infiltration was first observed at 12 h after inoculation, and a few PMNs could be seen in the epithelium at 24 h. Electron microscopic analysis at 24 h showed that virtually all inclusions were at the same stage of development, indicating a synchronous infection. Several chemokine and cytokine genes were expressed as early as 3 h after infection, but by 12 h, 41 genes were expressed. Thus, activation of the host response occurs both with the introduction of elementary bodies into the host and early replication of reticulate bodies. No significant response was observed when UV-inactivated organisms were inoculated into the cervix at any time interval. This model provides an ideal opportunity to investigate the mechanisms by which the early inflammatory response is induced in vivo.

Histopathologic response in the mouse endocervix following intracervical inoculation of chlamydiae. (A) Hematoxylin-and-eosin-stained section of the endocervix at 12 h after inoculation, showing three PMNs in a venule (circle and arrow). Magnification, ×25. (B) Hematoxylin-and-eosin-stained section of the endocervix at 24 h after inoculation. Many PMNs are now visible in venules and capillaries as well as the submucosa. Magnification, ×25. (C) Section of endocervix at 24 h after inoculation stained with antibody to chlamydial LPS and visualized by immunohistochemistry, showing several chlamydial inclusions (arrows). PMNs are also visible in the epithelium and submucosa. Magnification, ×25.

Flow cytometrical analysis of the cervices of mice at 24 h after intracervical inoculation. PMNs were significantly greater in the cervices of infected animals then in those of sham-inoculated animals (one-tailed t test). The bars represent the mean results for amounts in four animals (infected) and three animals (sham) ± standard deviation.

Ultrastructure of C. muridarum-infected mouse cervix 24 h postinoculation. (A) Multiple early inclusions, containing one or a few RB (arrows), are visible in superficial epithelial cells; no PMNs are seen in this area of the tissue. (B) In other tissue sites, a few PMNs (stars) can be seen migrating to the epithelial layers, eventually (C) targeting chlamydia-infected epithelial cells. Magnification, ×3,900; bars, 1 μm.

Increase in transcripts of chemokine receptor genes at 3, 12, and 24 h after intracervical inoculation. Only chemokine receptor genes with a twofold or greater increase are shown. Significant differences (P < 0.05 or less) compared to sham-inoculated animals are designated by *.

Increase in transcripts of CC chemokine genes at 3, 12, and 24 h after intracervical inoculation. Only genes with a twofold or greater increase are shown. Significant differences (P < 0.05 or less) compared to sham-inoculated animals are designated by *.

Increase in transcripts of CXC chemokine genes and complement factor 3 at 3, 12, and 24 h after intracervical inoculation. Only genes with a twofold or greater increase are shown. Significant differences (P < 0.05 or less) compared to sham-inoculated animals are designated by *.

Increase in transcripts of cytokine genes at 3, 12, and 24 h after intracervical inoculation. Only cytokine genes with a twofold or greater increase are shown. Significant differences (P < 0.05 or less) compared to sham-inoculated animals are designated by *.